COHORT PROFILE Cohort Profile: The Dutch ‘TRacking Adolescents ’ Individual Lives ’ Survey’; TRAILS

How did the study come about? Mental disorders account for one-fifth of the total burden of disease in the Western world,1 and, as such, should require due attention from the international epidemiological research community. Good quality research on the aetiology and course of psychopathol-ogy in the population is impossible without reliable and valid data from long-term longitudinal cohort studies. Research on psychopathology in adolescence is important both from a scientific point of view and from the point of view of prevention and public health policy. Adolescence is characterized by major biological, psychological and social challenges and opportunities, where interaction between the indivi-dual and environment is intense, and developmenta